Yes i will be using rubber feet. Approx 15-20mm high that will sink about 1,5-2mms under the weight of the subs. This will ensure (mathematically) optimal decoupling and any resonances will be moved out of the audible range down to about 5-10hz.
Will be doing some free air measurements soon to check on the frequency response and more. Just from a little testing these small boxes have remarkably high output and have a nice clean sound. I like them a lot from the little testing i've been doing.
@Rotebass: Cubo 18 and Cubo Sub are roughly in the same sensitivty ballpark, this is also a bit driver dependant of course. Cubo Sub drops considerably lower though (for those interested in heavy bass).
The RCF LF18X451 has a good balance between efficiency and excursion, meaning it will work in both Cubo 18 and Cubo Sub. I've used a similar driver in Cubo 18 recently and with 1800 Watts it was definately unlike other Cubo 15 and 18 experiences. In fact it came closer to the vibrations felt with Cubo Sub, so putting it in Cubo Sub in the first place would be a good choice.
@T.geessounds: A textbook example of how I would like to see every Cubo build, how does it fare?
@Welovit: Please, no. I mean, yes it would work but please don't. It all looked good till I saw the Qes and the physical weight. How about the Thomann 18 500? On paper it almost looks to good to be true.